The article “Edge-Preserving Smoothers for Image Processing” by C. K. Chu et al., Journal of the American Statistical Association, Vol. 93, No. 442, pp. 526-541, June 1998 discloses a filtering method, which is adapted to perform a filtering of an image such that undesirable noise is reduced while preserving edges. However, if the CNR (contrast-to-noise ratio) is too small in the image, edges may not be observable and may not be preserved, leading to a blurring of the image and, thus, to a decreasing image quality.